I have stock 914 rotors drilled to 5 lug in the rear. I just bought 914-6 rotors. how much does the OD need to be machined? The thickness is also larger. Will this fit in the stock calipers? I put the 914-6 rotors on the drilled out axles and the set screws did'nt line up. should I drill and tap new holes? Any information would be apprecitated.

they should fit inside the calipers NO problem....

im running the same setup, and i didnt touch the OD of the rotor... or the caliper....

worst case scenario, sand/file/grind the caliper, so you dont have to machine everyset of rotors....

I, have 914/6 rotors on my car, they are a little larger, but still fit the 914/4 rotor. The only thing, the 914/4 brake pads, don't ride the the edge of the rotor, apparently smaller.

You, could drill and tap for set screws, I, didn't.

QUOTE

I have stock 914 rotors drilled to 5 lug in the rear. I just bought 914-6 rotors. how much does the OD need to be machined?

Generally it doesn't. From what I've amassed, only about 5% of the cases require machining. Try it first.

QUOTE

The thickness is also larger. Will this fit in the stock calipers?

Yes.

QUOTE

I put the 914-6 rotors on the drilled out axles and the set screws did'nt line up. should I drill and tap new holes?

This is a slight problem. Porsche 5-lug hubs and Porsche (VW) 4-lug hubs don't use the same spacing for those rotor mounting screws. The screws are not important in the everyday function of the rotor. However, the only time I see this as an issue is when you're setting your venting clearance. I would:

1. Use 2 open ended lug nuts and seat the rotor with those and then set your venting clearance -or-
2. Drill the hubs as you mentioned and be done with it.